Telephone system.



E. A. GRAHAM.

TELEPHON E SYSTEM. APPLICATION Flu-in NOV- 18, 1914.

1,21 1,435. Patented Jan. 9, 1917.

2 SHEETS-SHEET I.

E A. GRAHAM.

TELEPHONE SYSTEM,

APPLiCATlON FILED NOV-18.1914.

1,21 1,435. Patented Jan. 9,1917.

2 SHEETSSHEET 2.

EDWARD ALFRED GRAHAM, OF BROCKLEY, LONDON, ENGLAND.

TELEPHONE SYSTEM;

' Specification of Letters Patent.

Patented Jan. 9, 1917.

Application filed November 18, 1914. Serial No. 872,818.

To all whom it may concern.-

Be it known that I, EDWARD ALFRED GRA- HAM, a subject of the King of Great Britain and Ireland, residing at Brockley, in the county of London, England, have invented Improvements in or Relating to Telephone Systems, of which the following is a specification.

This invention relates to telephonic apparatus more especially of the loud speaklines should possess inductance of a certain value with the object of preventing the noise of commutation in the machine generated supply from being reproduced in the telephone receivers, of preventing the reproduction in the telephone circuit of disturbances in any other part of the circuit and of preventing cross-speaking or overhearing as between different pairs of telephones in use at the same time.

iWhilc inductance inserted in the telephone supply lines has the aforesaid efiect it would at the same time prevent the proper functioning of the telephone transmitter when. connected in series with the, telephonic receiver of an instrument placed in communication therewith were not provision made to avoid this.

Now the object of the present invention is to enable the fluctuations set up by and consequent upon the use of the transmitter in one telephone instrument to be reproduced in the receiver of another telephone instrument with full efiiciency irrespective of the value of inductance in the circuit. For this purpose a condenser or equivalent electrical capacity such as an electrolytic polarization cell (hereinafter referred to as a condenser) isconnected in parallel with the circuit or portion of the circuit including the transmitter of one instrument and the receiver of another instrument, being a direct shunt across the source of current in such a mannerthat a transmitter and receiver circuitis established which excludes the inductances and in which the fluctua tlons or certain of the fluctuations occasloned by the functioning of the telephonic elements take place without necessarily traversing the inductance-containing portion of the circuit, the condenser allowing the passage of a fluctuatory current complementary to that occasioned by the functioning of the transmitter of the tele-' phone circuit thereby permitting current variations in such circuit while admitting of a steady or substantially steady feeding current flowing through the windings of the inductance.

The condenser or condensers according to the present invention may be located at a central position and be permanently connected across the supply leads either or both of which includes or include an inductance or inductances, or the condenser or condensers may be placed within the casings of the telephone instruments as may be found convenient.

The specification of British Letters Patent No. 3935 of 1907 granted to me describes means providing for satisfactory speech reproduction in series transmitter and receiver circuits, notwithstanding the inductance included in the supply circuits, but the present invention is intended to accomplish a like result without necessitating a continuous flow of current, except in the actual speaking circuits, and therefore constitutes a useful improvement thereon inasmuch as possible waste of electrical energy is avoided.

In the accompanying drawings, Figures 1 to 6 inclusive respectively illustrate diagrammatically various circuit arrangements according to the invention as hereafter more specifically referred to.

In Fig. 1 a simple circuit is shown wherein the instrument at station A has a transmittei' a but no receiver, connected to an instrument at station B having a receiver 5 but no transmitter, a condenser c beingarranged as a shunt across the supply leads d and e. WVhen the circuit is completed by closure of the switch contacts at a direct current will flow from the positive pole of the source of electric supply through the supply lead d, and conductor (Z and through tained irrespective of the variations taking place in the stud transmitter-receiver c1rcuit. In the case Where each instrument is provided with a transmitter a and a receiver b, as diagrammatically shown in Fig. 2, each instrument is supplied with current from one of the leads and conductors which in-- cludes inductance, in this instance the positive conductor 03, the said inductance being shown as in the form of two separate coils 03 arranged at or near each instrument. The circuit is as set forth in connection with Fig. 1, the negative conductor 6 forming a common return for both transmittter-rereceiver circuits.

It may be advantageous in some cases to employ only three conductors between a pair of instruments placed in communication and an example of such connection, embodying the present invention, is shown in Fig. 3, where as and I) represent transmitters and receivers, respectively, in the instruments at stations A and B. In this case an inductance (Z is placed in the supply lead d and conductor (Z is connected to the common junction of the transmitter a and receiver 7) of the instrument at station A. The condenser c is connected between the telephone side of the inductance (l and the negative supply lead 6. When station A communicates with station B by completing the circuit through switch contacts (1 the current will flow from the positive lead d through the inductive winding 0Z conductor d through the transmitter a at station A, along conductor f, through receiver windings Z) at station 7) and from thence to the conductor 6 and negative lead 6. Upon the transmitter functioning as previously referred to, complementary fluctuatory currents will flow through the condenser c and satisfactory speech reproduction will be obtained in the same manner as in the other arrangement hereinbefore described. In a like manner communication can be made from the transmitter a. at station B to the receiver 6 at station A.

In some installations it is essential that, in addition to a voice call, as set forth in connection with the circuits herein previously described, a bell or other audible signal should be provided. For an example of a circuit in which voice and bell calls are obtainable, reference is made to Fig. 4c. lln this-case the transmitter-receiver circuits are substantially as described in connection with Fig. 2 except that additional switch contacts are required. The functioning of each of the circuits mentioned is as follows: To originate a bell signal at station A the push indicated at i of the instrument at station A is depressed. Current will then flow from the positive lead cl, through inductance 0Z conductors (1 through the lower contact at i of switch 2', along conductor g, through tance 6Z2, conductor (Z through the transmitter a, along conductor f, through the top contact 2' of the switch i at station B, through receiver 6 at such station and thence through the conductor 6 to the negative lead 6. The condenser 0, shown as divided in two sections, being connected to the telephone side of the inductance (l and thence to the negative supply lead 6, will function in the manner hereinbefore set forth. A corresponding speaking circuit may be completed when communication by voice is required from station B to station A. In the several arrangements hereinbefore described plain inductances are shown inserted in the supply leads or conductors but it will be understood that a repeater coil, as frequently used in telephone systems, may be applied in lieu of such plain inductances. A simple circuit including a repeater coil in the positive supply lead is shown in Fig. 5. In this case, assuming it is desired to communicate from the instrument at station A to the instrument at station B the circuit is completed at the switch a of the instrument atstation A and current will flow from the positive supply lead 01 through one winding of the repeater coil (1 through the transmitter a, along conductor f, through the receiver winding b tothe negative supply lead 6 and the complementary fluctuatory current will flow through the second winding of the repeater coil (1 and through the condenser 0 to the negative supply lead 6, the condenser functioning in the manner hereinbefore set forth.

In the several arrangements hereinhefore described, an inductance'coil or coils or other telephonic coils is or are indicated as being inserted in the positive supply lead only, solely by Way of example, but it will be understood that such inductance or other telephonic coil or coils can be inserted in the negative supply lead or in both the positive and negative supply leads. Also, it will be understood that signal bells or other audible calling devices, visual signaling devices or relay de ices, such as are associated with telephonic circuits, can be ap lied in various known ways to the telephonic circuits hereinbefore referred to without departing from the essential feature of the present invention and as hereinafter described. It will be further understood that the arrangement of telephonic apparatus as herein set forth can be applied in known ways forcommunication through a central exchange or in connection with switching devices enabling one station to communicate with several stations. An instance of this kind is shown in Fig. 6, which at the same time illustrates a detail modification associated with the receivers b which are shown as bridging, each in series with a condenser is, an inductance m that is included in the leads 7, e Jacks in the exchange, associated with the several instruments, are indicated at u, 'v, a" permanently connected to the leads as shown, and 1, 2 represent plugs for use with the several jacks. Assuming that neither plug is in use, then closure of the switch a at station A will permit current to flow from the supply,

lead 03 through the inductance d lead (1 switch a transmitter a, lead 7 and jack springs 20 which are normally in contact, and lead f to the exchange receiver 6 (station C) and thence by leads 6 to the negative supply lead a.

s is a vibrator which can be substituted for the transmitter a in the circuit described by closing switch 8 in lieu of switch (1 thereby substituting a hooter call for a voice call. A similar circuit can be traced through the jack '0 when station B is calling the exchange C. With plug 1 in jack to and plug 2 in the jack '2), conversation can be carried on between station A and station E, the circuit being completed from lead f and one of the jack springs 14 for station A through jack spring 3 for station B and'thence by lead f receiver 7) and lead 6 to the negative supply lead 6. At the exchange C a vibrator s is shown so arranged that normally, with the speaking key to open, the act of inserting either the plug 1 or plug 2 in jack x will result in a circuit being completed by way of the positive lead d, inductance d switch w the vibrator s and jack spring t through the plug 1 or 2 to either station B or A, the receiver circuit 5 being completed as already described so that a hooting call continues. By reversing the position of the switch-w at the exchange C, the transmitter a thereat can be substituted for the vibrator s,whereupon the hooting call ceases.

e in Fig. 6 shows an inductance in the supply lead e. The inductances m at stations A and B take, as shown, the form of relays each adapted to close a signal circuit such as the circuit of a lamp n and bell 0 connected in parallel either of which may, however, be omitted if so desired. The inductances d associated with the instruments of stations A and B but located at the exchange C and bridged by the condensers 0 according to the invention also take the form of relays each adapted to complete the circult of a corresponding signal, as for'instance a lamp ,p, to indicate at the exchange the station A or B that may be calling.

What I claim is I .1. A telephonic system comprising a transmitter at one station, a receiver at a companlon station,-a source of current common to both stations, positive and negative supply leads, means possessing inductance, connections including positive and negative leads adapted to supply direct current to the transmitter and receiver aforesaid through the said inductance and means, preventing the flow of unidirectional current, connected in parallel with the transmitter and receiver circuit aforesaid when the latter is a complete, such means being a direct shunt supply leads having inductance in at least one of them, leads adapted to operatively connect the transmitter to the receiver and both of these to the supply leads and means, preventing the flow of unidirectional current, connected in parallel with the transmitter and receiver circuit aforesaid, such means being a direct shunt across the source of current for the purpose set forth.

3. A telephonic system comprising a transmitter at one station, a receiver at a companion station, a source of current com mon to both stations, positive and negative supply leads containing inductance, leads adapted to operatively connect the transmitter to the receiver and both of these to the supply leads and means, preventingzthe flow of unidirectional current, arranged as a shunt across the supply leads at the telephone si'de of the inductance aforesaid, the said means being thus in parallel with the transmitter and receiver circuits and a direct shunt across the source of current.

4. A telephonic system comprising a transmitter at one station, a receiver at a companion station, a source of current common to both stations, positive and negative supply leads having inductance in at least one of them, leads adapted to operatively connect the transmitter to the receiver and both of these to the supply leads and a condenser arranged as a shunt to the source of current across the supply leads at the telephone side of the inductance aforesaid.

5. A telephonic system comprising a current, connected in parallel with the transmitter and receiver circuit aforesaid, such means being a direct shunt across the source of current. 15 Signed at London v England, this twelfth day of October, 1914.

EDWARD ALFRED GRAHAM.

Witnesses EDMUND EUGENE BARNARD, HENRY WILLIAM DEJUNE. 

